Flame retardant block copolymers from renewable feeds

ABSTRACT

A flame retardant block copolymer is prepared from renewable content. In an exemplary synthetic method, a bio-derived flame retardant block copolymer is prepared by a ring opening polymerization of a biobased cyclic ester and a phosphorus-containing polymer. In some embodiments, the biobased cyclic ester is lactide. In some embodiments, the phosphorus-containing polymer is a hydroxyl-telechelic flame retardant biopolymer prepared by a polycondensation reaction of a biobased diol (e.g., isosorbide) and a phosphorus-containing monomer (e.g., phenylphosphonic dichloride). In other embodiments, the phosphorus-containing polymer is synthesized from a dioxaphospholane monomer.

BACKGROUND

The present invention relates in general to the field of flameretardancy. More particularly, the present invention relates to flameretardant block copolymers prepared from renewable feedstock.

SUMMARY

In accordance with some embodiments of the present invention, a flameretardant block copolymer is prepared from renewable content. In anexemplary synthetic method, a bio-derived flame retardant ABA-typetri-block copolymer is prepared by a ring opening polymerization of abiobased cyclic ester and a phosphorus-containing polymer. In someembodiments, the biobased cyclic ester is lactide. In some embodiments,the phosphorus-containing polymer is a hydroxyl-telechelic flameretardant biopolymer prepared by a polycondensation reaction of abiobased diol (e.g., isosorbide) and a phosphorus-containing monomer(e.g., phenylphosphonic dichloride). In other embodiments, thephosphorus-containing polymer is a polyphosphoester synthesized from aring opening polymerization of a dioxaphospholane monomer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Embodiments of the present invention will hereinafter be described inconjunction with the appended drawings, where like designations denotelike elements.

FIG. 1 is a block diagram illustrating an exemplary printed circuitboard (PCB) having layers of dielectric material that incorporate abio-derived flame retardant block copolymer in accordance with someembodiments of the present invention.

FIG. 2 is a block diagram illustrating an exemplary connector having aplastic housing and an exemplary plastic enclosure panel each of whichincorporates a bio-derived flame retardant block copolymer in accordancewith some embodiments of the present invention.

DETAILED DESCRIPTION

The use of synthetic polymers from petroleum sources is widespread.Petroleum-derived synthetic polymers can be found in nearly every itemwe use in our daily lives. There is a growing shift to prepare polymericmaterials from renewable feedstock because petroleum is a finiteresource. The use of these renewable polymers is envisaged inapplications from disposable products to durable goods. However,significant challenges must be overcome before renewable polymers findwide spread use. One of the main challenges facing renewable polymers isflame retardancy. Known renewable polymers and polymer blends containingrenewable polymers typically do not retard burning. There is asignificant paucity of inherently flame retardant renewable polymers,despite the need for flame retardant characteristics in manyapplications. A common approach to render renewable polymers and blendscontaining renewable polymers as flame retardant is to incorporate flameretardant additives such as halogenated or phosphorus-containingmaterials. These flame retardant additives are typically small moleculesand are in the form of particles. Necessary loadings of these flameretardant additives can run as high as 30%, thus compromising themechanical properties of the resulting composite materials.

Traditional renewable materials, such as vegetable oils, fatty acids,starch, cellulose and natural rubber, have been available for decades.More recently, a new class of biobased starting compounds has becomeavailable. For example, isosorbide, which is a biobased monomer obtainedfrom starch extracted from corn (or other starch source), iscommercially available from suppliers and agricultural processors suchas Archer Daniels Midland Company (ADM). Large scale availability ofadditional biobased monomers through improved production processes, aswell as the development of a biobased product infrastructure, willaccelerate the shift toward the use of renewable feedstock.

Isosorbide (IS) is a so-called 1,4:3,6-dianhydrohexitol (DAH). Moregenerally, 1,4:3,6-dianhydrohexitols (DAHs) include:1:4:3,6-dianhydro-D-glucitol (isosorbide, IS);1,4:3,6-dianhydro-L-iditol (isoidide, II); and1,4:3,6-dihydro-D-mannitol (isomannide, IM).

Isosorbide (IS) has the following molecular structure:

Isoidide (II) has the following molecular structure:

Isomannide (IM) has the following molecular structure:

Each of the DAHs can be obtained from biomass. Isosorbide (IS) iscurrently the most widely commercially available DAH.

In addition to DAHs, many other monomers can be obtained from biomass.Such renewable monomers include 2,5-bis(hydroxymethyl)furan, ethyleneglycol, propylene glycol (also referred to as “1,2-propanediol”),1,3-propanediol, glycerol (also referred to as “glycerin” and“glycerine”), 2,3-butanediol, lactic acid, succinic acid, citric acid,levulinic acid, lactide, and ethanol. Among the monomers that can beobtained from biomass are biobased diols (e.g., DAHs,2,5-bis(hydroxymethyl)furan, ethylene glycol, propylene glycol,1,3-propanediol, glycerol, and 2,3-butanediol), any one of which may beemployed as a reactant in accordance with some embodiments of thepresent invention.

Some bio-derived polymers are already being produced on a commercialscale (e.g., polylactic acid (PLA)), but tailoring these materials tospecific applications requires overcoming several technologicalchallenges. For example, as mentioned earlier, there is a significantpaucity of inherently flame retardant renewable polymers, despite theneed for flame retardant characteristics in many applications. Whileflame retardants with some renewable content are known, such flameretardants have very little renewable content and are immiscible withchemically inequivalent commercial bioderived polymers, such aspolylactic acid. One example of a known flame retardant with somerenewable content is poly(DPA-PDCP) obtained through interfacialpolycondensation between diphenolic acid (DPA) and phenyldichlorophosphate (PDCP). Another example of a known flame retardantwith some renewable content is poly(MDP-PDCP-MA) synthesized through azinc acetate catalyzed reaction of melamine (MA) and poly(MDP-PDCP),which is obtained through interfacial polycondensation between methyldiphenolate (MDP) and phenyl dichlorophosphate (PDCP). These known flameretardants have very little renewable content. Both of these known flameretardants use diphenolic acid as one of the raw materials, which may bederived (in part) from levulinic acid (which, as noted above, is amongthe monomers that can be obtained from biomass). However, the vastmajority of the mass of diphenolic acid is obtained frompetroleum-derived feedstock. These known flame retardants have no otherrenewable content. Moreover, these known flame retardants are immisciblewith chemically inequivalent commercial bioderived polymers, such aspolylactic acid.

For purposes of this document, including the claims, the term “biobased”refers to chemicals, energy sources and other materials that utilizebiological or renewable agricultural material. Also, for purposes ofthis document, including the claims, the term “renewable” refers to achemical, energy source or other material that is inexhaustible orrapidly replaceable by new growth. Also, for purposes of this document,including the claims, the term “biomass” refers to a biological materialderived from living, or recently living organisms.

In the manufacture of PCBs, connectors, electronic device plasticenclosures and plastic enclosure panels, and other articles ofmanufacture that employ thermosetting plastics (also known as“thermosets”) or thermoplastics, incorporation of a flame retardant isrequired for ignition resistance. Typically, brominated organiccompounds impart flame retardancy. Consequently, the base material(e.g., epoxy resin for PCBs, and liquid crystal polymer (LCP) forconnectors, and acrylonitrile butadiene styrene (ABS) for electronicdevice plastic panels and plastic enclosure panels) properties arecompromised because a relatively large quantity of a flame retardant isnecessary to achieve the desired ignition resistance.

In accordance with some embodiments of the present invention, a flameretardant block copolymer is prepared from renewable content. In anexemplary synthetic method, a bio-derived flame retardant ABA-typetri-block copolymer is prepared by a ring opening polymerization of abiobased cyclic ester and a phosphorus-containing polymer.

In some embodiments, the biobased cyclic ester is lactide. For example,lactide is used in the second step of reaction schemes 1, 2 and 3,described below.

In some embodiments, the phosphorus-containing polymer is ahydroxyl-telechelic flame retardant biopolymer. For example, ahydroxyl-telechelic flame retardant biopolymer is used in the secondstep of reaction schemes 1 and 2, described below.

The hydroxyl-telechelic flame retardant biopolymer may be a cyclicphosphonate prepared by a polycondensation reaction of a biobased diol(e.g., isosorbide) and a phosphorus-containing monomer (e.g.,phenylphosphonic dichloride). The biobased diol may be obtained eitherdirectly from, or through modification of, a biological product.Preferably, at least 50% of the mass of the biobased diol is obtaineddirectly from a biological product. More preferably, the entire mass ofthe biobased diol is obtained directly from a biological product. Thephosphorus-containing monomer may be a phosphonic dichloride,dichlorophosphate, alkyl/aryl phosphonate, or otherphosphorus-containing monomer known for flame retardancy (e.g., aphosphinate, a phosphonate, a phosphate ester, and combinationsthereof). For example, a hydroxyl-telechelic flame retardant biopolymeris synthesized using melt-based condensation polymerization in the firststep of reaction scheme 1, described below, and solution-basedcondensation polymerization in the first step of reaction scheme 2,described below.

In other embodiments, the phosphorus-containing polymer is apolyphosphoester (e.g., a polymeric phosphate ester) derived from adioxaphospholane monomer. For example, a polyphosphoester is used in thesecond step of reaction scheme 3, described below.

The polyphosphoester may be prepared by a ring opening polymerization ofa dioxaphospholane monomer. For example, a polyphosphoester issynthesized using a ring opening polymerization in the first step ofreaction scheme 3, described below.

Flame retardant ABA-type tri-block copolymers in accordance with someembodiments of the present invention are defined by aphosphorus-containing flame-retardant “B-block” polymer (whichpreferably contains some renewable content) and an “A-block” comprisedof bioderived polymers (e.g., polylactic acid). An exemplary bio-derivedflame retardant tri-block copolymer (synthesized in reaction scheme 2,described below) in accordance with some embodiments of the presentinvention has the following ABA-type molecular structure:

However, bio-derived flame retardant block copolymers in accordance withsome embodiments of the present invention need not be ABA-type tri-blockcopolymers. Flame retardant ABA-type tri-block copolymers in accordancewith some embodiments of the present invention are set forth in thisdocument for purposes of illustration, not limitation. Bio-derived flameretardant block copolymers in accordance with some embodiments of thepresent invention include AB diblock copolymers, ABA tri-blockcopolymers all the way through

AB

multiblock copolymers.

Bio-derived flame retardant block copolymers in accordance with someembodiments of the present invention, used directly or blended with the“A-block” homopolymer, yield flame-retardant materials that may bederived predominately from renewable content. Furthermore, the tri-block(or diblock or multiblock) structure ensures either a homogeneous ornano/microstructured incorporation of the bio-derived flame retardantblock copolymer throughout the bulk material, resulting in optimal flameretardancy and mechanical strength.

In accordance with some embodiments of the present invention, flameretardant moieties are incorporated directly into the renewable polymerbackbones. Condensation polymerization of a biobased diol such asisosorbide and a phosphorus-containing monomer such as phenylphosphonicdichloride, for example, incorporates flame retardant moieties (i.e.,phosphorus) directly into the backbone of the resulting bio-derivedflame retardant polymer (i.e., the B-block). The resulting homogeneousand uniform incorporation of phosphorus yields flame retardantbio-derived polymers without the need for discrete particles (i.e.,conventional flame retardant additives) that often come with the caveatof diminished mechanical toughness, stiffness, etc. Additionally,because these bio-derived flame retardants are polymers and not smallmolecules (conventional flame retardant additives typically are smallmolecules), the mechanical properties of the composite will not becompromised.

In accordance with some embodiments of the present invention,bio-derived flame retardant block copolymers may be used alone orblended with other polymers. For example, a bio-derived flame retardantblock copolymer in accordance with some embodiments of the presentinvention may be blended with one or more petroleum-derived polymers(e.g., acrylonitrile butadiene styrene (ABS)) and/or one or moreconventional bio-derived polymers (e.g., polylactic acid (PLA),polyhydroxybutyrate (PHB), and the like). For example, a bio-derivedflame retardant block copolymer in accordance with some embodiments ofthe present invention may be blended with a renewable-based compositepolymer, such as a mixture of polyhydroxybutyrate (PHB) bioplastic andcarbon dioxide-based polypropylene carbonate (PPC) (containing 43% byweigh CO₂), which is a renewable-based composite polymer alternative forABS developed by Siemens.

Alternatively, in accordance with other embodiments of the presentinvention, bio-derived flame retardant block copolymers may be used asflame retardant additives (i.e., discrete particles) in compositematerials. For example, a bio-derived flame retardant block copolymermay be ground to particles that may serve as a flame retardant additivein a composite material. These bio-derived flame retardant blockcopolymer particles may also serve to increase the renewable content inthe composite material as compared to conventional flame retardantadditives that lack renewable content.

An exemplary printed circuit board (PCB) implementation of the presentinvention is described below with reference to FIG. 1, while anexemplary connector implementation and an exemplary plastic enclosurepanel implementation of the present invention are described below withreference to FIG. 2. However, those skilled in the art will appreciatethat the present invention applies equally to any manufactured articlethat employs thermosetting plastics (also known as “thermosets”) orthermoplastics.

As described below, a bio-derived flame retardant block copolymer inaccordance with some embodiments of the present invention may besynthesized by, for example, a polycondensation reaction in the melt ofa biobased diol and a phosphorus-containing monomer and, subsequently, aring opening polymerization of a biobased cyclic ester and thepolycondensation reaction product. This first pathway to prepare abio-derived flame retardant block copolymer in accordance with someembodiments of the present invention is exemplified by reaction scheme1, below.

However, those skilled in the art will appreciate that a bio-derivedflame retardant block copolymer in accordance with some embodiments ofpresent invention may be synthesized using other processes and reactionschemes. For example, a bio-derived flame retardant block copolymer inaccordance with some embodiments of the present invention may besynthesized by, for example, a polycondensation reaction in solution ofa biobased diol and a phosphorus-containing monomer and, subsequently, aring opening polymerization of a biobased cyclic ester and thepolycondensation reaction product. This second pathway to prepare abio-derived flame retardant block copolymer in accordance with someembodiments of the present invention is exemplified by reaction scheme2, below.

In another example, a bio-derived flame retardant block copolymer inaccordance with some embodiments of the present invention may besynthesized by, for example, a ring opening polycondensation of adioxaphospholane to obtain a polyphosphoester and, subsequently, a ringopening polymerization of a biobased cyclic ester and thepolyphosphoester. This third pathway to prepare a bio-derived flameretardant block copolymer in accordance with some embodiments of thepresent invention is exemplified by reaction scheme 3, below.

The first pathway is exemplified below in the non-limiting reactionscheme (i.e., reaction scheme 1). A reaction scheme (reaction scheme 1)follows for synthesizing a bio-derived flame retardant block copolymerin accordance with some embodiments of the present invention through 1.)a melt-based condensation polymerization of a biobased diol and aphosphorous-containing monomer and, subsequently, 2.) a ring openingpolymerization of a biobased cyclic ester and the polycondensationreaction product. In the first step of reaction scheme 1, isosorbide andphenylphosphonic dichloride are reacted via condensation polymerizationin a melt state. In the second step of reaction scheme 1, thebio-derived flame retardant polymer reaction product of the condensationpolymerization and lactide are reacted via ring opening polymerization.

In the first step of reaction scheme 1, a bio-derived flame retardantpolymer is synthesized through a melt polycondensation reaction ofisosorbide and phenylphosphonic dichloride using conventional procedureswell known to those skilled in the art. The first step of reactionscheme 1 may be performed at 150° C. while stifling under a vacuum(e.g., 1-5 mbar) for several hours (e.g., 4 hours). Generally,stoichiometric quantities of the reactants may be used.

Melt polycondensation techniques are well known in the art. For example,a thesis by Bart A. J. Noordover, “Biobased step-growthpolymers—chemistry, functionality and applicability”, TechnischeUniversiteit Eindhoven, 2007, discloses melt polycondensation techniquesin the context of synthesizing biobased step-growth polymers for athermosetting powder coatings. The Noordover thesis is herebyincorporated herein by reference in its entirety.

The bio-derived flame retardant polymer (i.e., the B-block) synthesizedthrough the melt polycondensation reaction is made with hydroxylendgroups, which are used as handles to subsequently grow additionalbioderived polymers (i.e., the A-blocks). This may be accomplished by,for example, adjusting the quantity of the reactants used in the meltpolycondensation reaction so that isosorbide is slightly in excessrelative to the stoichiometric quantity. The endblock polymers (i.e.,the A-blocks) enhance compatibility of the renewable flame retardantwith the surrounding matrix in order to inhibit macrophase separation ofthe flame retardant into larger particles, which often leads todiminished mechanical properties in polymers.

Optionally, an inert gas (e.g., N₂) may be flowed through the reactor tolimit oxidation and facilitate removal of HCl vapor formed during thereaction.

Also, a catalyst dissolved in a solvent may be optionally added to themelt. For example, tin(II) 2-ethylhexanoate (also referred to as“Sn(Oct)₂”) or titanium(IV) n-butoxide (0.02 mol % relative tophenylphosphonic dichloride), dissolved in toluene, may be added to themelt. Zinc(II) and titanium(IV) catalysts may also be used, as well asorganic catalysts, such as 4-dimethylaminopyridine (DMAP),1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) and triazabicyclodecene (TBD).

Isosorbide is a commercially available biobased diol. As mentionedabove, isosorbide is a biobased monomer obtained from starch extractedfrom corn (or other starch source). Isosorbide, which is a solid at roomtemperature, is well suited for melt polycondensation reactions.Isosorbide has a melting point temperature between 60 and 63° C., and isstable up to 270° C. In addition, isosorbide is hygroscopic.

Phenylphosphonic dichloride is a commercially availablephosphorus-containing monomer. Phenylphosphonic dichloride is a liquidat room temperature. Phenylphosphonic dichloride has a meltingtemperature of 3° C., and has a boiling temperature of 258° C.

Typically, after the melt polycondensation reaction is complete, thebio-derived flame resistant polymer is removed from the reactor, washedand dried. For example, the reaction product may be precipitated into anappropriate non-solvent (e.g., methanol) and washed with non-solvent.The reaction product may then be dried under vacuum for twenty-fourhours at room temperature.

In second step of reaction scheme 1, a bio-derived flame retardant blockcopolymer is synthesized through a ring opening polymerization oflactide and the phosphorus-containing polymer (synthesized in the firststep of reaction scheme 1) using conventional procedures well known tothose skilled in the art. The second step of reaction scheme 1 may beperformed in the presence of stannous octoate (Sn(Oct)₂) as a catalystand toluene as a solvent. Generally, stoichiometric quantities of thereactants may be used.

Ring opening polymerization techniques are well known in the art. Forexample, U.S. Patent Application Publication No. 2011/0223206 A1, toLEBOUILLE et al., entitled “MICELLE COMPOSITIONS AND PROCESS FOR THEPREPARATION THEREOF”, published Sep. 15, 2011, discloses ring openingpolymerization techniques in the context of a micelle composition. TheLEBOUILLE et al. patent application publication is hereby incorporatedherein by reference in its entirety.

For example, in the second step of the first reaction scheme, thebio-derived flame resistant polymer from the first step may be weighedinto a two-necked round bottle flask, and subsequently placed in an oilbath at 150° C. A vacuum is employed before continuing synthesis.Lactide may be added to the bio-derived flame resistant polymer byremoving the vacuum and simultaneously flushing with nitrogen gas. Thevacuum is then reapplied, and the reactants are stirred. Once ahomogeneous melt is obtained, stannous octoate (Sn₂Oct) dissolved intoluene may be added to the reactants by removing the vacuum andsimultaneously flushing with nitrogen gas. The vacuum is then reapplied.The reaction conditions are maintained for a few hours, after which thevacuum is replaced with nitrogen gas.

Alternatively, the second step of the first reaction scheme can be donewith the same reagents in refluxing toluene, which would takeapproximately 24 hours. Toluene is not necessarily preferred over meltpolymerization.

Alternatively, the second step of the first reaction scheme can be donewith the same reagents in most any aprotic solvent between 0-35° C. withthe more reactive organic catalysts (e.g., DMAP, DBU and TBD).

A catalyst dissolved in a solvent is added to the reactants. Forexample, tin(II) 2-ethylhexanoate (also referred to as “Sn(Oct)₂”) ortitanium(IV) n-butoxide (0.02 mol % relative to phenylphosphonicdichloride), dissolved in toluene, may be added to the reactants.Zinc(II) and titanium(IV) catalysts may also be used, as well as organiccatalysts, such as 4-dimethylaminopyridine (DMAP),1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) and triazabicyclodecene (TBD).

Lactide is a commercially available biobased cyclic ester monomer. Asmentioned above, lactide is a monomer that can be obtained from biomass.Lactide is the cyclic di-ester of lactic acid. Lactide may be preparedby heating lactic acid in the presence of an acid catalyst. Lactide,which is a solid at room temperature, has a melting point temperaturebetween 95 and 97° C.

Typically, after the ring opening polymerization is complete, thebio-derived flame resistant block copolymer is removed from the reactor,washed and dried. For example, the reaction product may be precipitatedinto an appropriate non-solvent (e.g., methanol) and washed withnon-solvent. The reaction product may then be dried under vacuum fortwenty-four hours at room temperature. Optionally, the reaction productmay now be crushed into particles, and re-dried under vacuum. Theresultant particles may be course particles, fine particles, ultrafineparticles, or nanoparticles.

Those skilled in the art will appreciate that reaction scheme 1 is setforth for the purpose of illustration not limitation. For example, thefirst step of reaction scheme 1 synthesizes a particular bio-derivedflame retardant polymer by a melt polycondensation reaction of aparticular biobased diol (isosorbide) and a particularphosphorus-containing monomer (phenylphosphonic dichloride). Thisparticular synthesis of this particular bio-derived flame retardantpolymer is exemplary. In general, a bio-derived flame retardant polymerin accordance with some embodiments of the present invention may besynthesized in the first step of reaction scheme 1 using apolycondensation reaction in the melt or in solution of any suitablebiobased diol and any suitable phosphorus-containing monomer.

Also, the second step of reaction scheme 1 synthesizes a particularbio-derived flame retardant block copolymer by a ring openingpolymerization of a particular biobased cyclic ester (lactide) and aparticular phosphorus-containing polymer (i.e., the bio-derived flameretardant polymer synthesized in the first step of reaction scheme 1).This particular synthesis of this particular bio-derived flame retardantblock copolymer is exemplary. In general, a bio-derived flame retardantblock copolymer in accordance with some embodiments of the presentinvention may be synthesized in the second step of reaction scheme 1using a ring opening polymerization of any suitable biobased cyclicester and any suitable phosphorus-containing polymer.

The second pathway is exemplified below in another non-limiting reactionscheme (i.e., reaction scheme 2). A reaction scheme (reaction scheme 2)follows for synthesizing a bio-derived flame retardant block copolymerin accordance with some embodiments of the present invention through 1.)a solution-based condensation polymerization of a biobased diol and aphosphorus-containing monomer and, subsequently, 2.) a ring openingpolymerization of a biobased cyclic ester and the polycondensationreaction product. In the first step of reaction scheme 2,phenylphosphonic dichloride and 2,5-bis(hydroxymethyl)furan are reactedvia condensation polymerization in solution. In the second step ofreaction scheme 2, the bio-derived flame retardant polymer reactionproduct of the condensation polymerization and lactide are reacted viaring opening polymerization

In the first step of reaction scheme 2, a bio-derived flame retardantpolymer is synthesized through a solution-based polycondensationreaction of 2,5-bis(hydroxymethyl)furan and phenylphosphonic dichlorideat room temperature (e.g., 25° C.) for several hours (e.g., 2 to 3hours) using conventional procedures well known in the art.2,5-bis(hydroxymethyl)furan is reacted with phenylphosphonic dichloridein the presence of triethylamine (NEt₃) (also referred to as “Et₃N”,“TEA” and “N,N-diethylethanamine”), 4-dimethylaminopyridine (DMAP), andtetrahydrofuran (THF) to form the bio-derived flame retardant polymer.NEt₃ and DMAP are catalysts. THF is the solvent. Generally,stoichiometric quantities of the reactants may be used.

2,5-bis(hydroxymethyl)furan is a commercially available biobased diol.As mentioned above, 2,5-bis(hydroxymethyl)furan is a monomer that can beobtained from biomass. 2,5-bis(hydroxymethyl)furan, which is a solid atroom temperature, has a melting point temperature between 74 and 77° C.

Phenylphosphonic dichloride is a commercially availablephosphorus-containing monomer. Phenylphosphonic dichloride is a liquidat room temperature.

NEt₃ and DMAP are commercially available organic catalysts. One skilledin the art will appreciate that any suitable catalyst (proton acceptor)may be used in lieu of, or in addition to, NEt₃ and DMAP. For example,tri-n-butylamine (TBA) is also a suitable catalyst.

THF is a commercially available solvent. One skilled in the art willappreciate that any suitable solvent may be used in lieu of, or inaddition to, THF. The choice of solvent is not critical as long as themonomers are soluble in the solvent. It is vital, however, that thesolvent not be alcoholic in nature to prevent unwanted side reactions ofreagents with the solvent. Acceptable solvents include, but are notlimited to, ether and polar aprotic solvents. The following solvents arethe most common: tetrahydrofuran, dimethylformamide, and acetonitrile.Further various other hydrocarbons solvents in which the monomers aremiscible may be used as cosolvents. One example of such a cosolvent isbenzene. Which solvent is preferred depends on the solubility of thesubject monomers. In many cases, the preferred solvent istetrahydrofuran.

Solution-based polycondensation techniques are well known in the art.For example, an article by Yan Liu et al., “DESIGN, SYNTHESIS, ANDAPPLICATION OF NOVEL FLAME RETARDANTS DERIVED FROM BIOMASS”,BioResources, Vol. 7, No. 4, 2012, pp. 4914-4925, disclosessolution-based polycondensation techniques in the context of flameretardants. The Liu et al. article is hereby incorporated herein byreference in its entirety.

The bio-derived flame retardant polymer (i.e., the B-block) synthesizedthrough the solution-based polycondensation reaction is made withhydroxyl endgroups, which are used as handles to subsequently growadditional bioderived polymers (i.e., the A-blocks). This may beaccomplished by, for example, adjusting the quantity of the reactantsused in the polycondensation reaction so that2,5-bis(hydroxymethyl)furan is slightly in excess relative to thestoichiometric quantity. The endblock polymers (i.e., the A-blocks)enhance compatibility of the renewable flame retardant with thesurrounding matrix in order to inhibit macrophase separation of theflame retardant into larger particles, which often leads to diminishedmechanical properties in polymers.

Precipitation into an appropriate non-solvent (e.g., methanol) is usedfor product isolation (i.e., to remove the reaction product from thesolvent).

After the solvent is removed, the reaction product is then washed anddried. For example, the reaction product may be washed with non-solventand then dried under vacuum for twenty-four hours at room temperature.

In second step of reaction scheme 2, a bio-derived flame retardant blockcopolymer is synthesized through a ring opening polymerization oflactide and the phosphorus-containing polymer (synthesized in the firststep of reaction scheme 1) using conventional procedures well known tothose skilled in the art. The second step of reaction scheme 2, as wellas the post-reaction processing, may be performed in the same manner asthe second step of reaction scheme 1.

Those skilled in the art will appreciate that reaction scheme 2 is setforth for the purpose of illustration not limitation. For example, thefirst step of reaction scheme 2 synthesizes a particular bio-derivedflame retardant polymer by a solution-based polycondensation reaction ofa particular biobased diol (2,5-bis(hydroxymethyl)furan) and aparticular phosphorus-containing monomer (phenylphosphonic dichloride).This particular synthesis of this particular bio-derived flame retardantpolymer is exemplary. In general, a bio-derived flame retardant polymerin accordance with some embodiments of the present invention may besynthesized in the first step of reaction scheme 2 using apolycondensation reaction in the melt or in solution of any suitablebiobased diol and any suitable phosphorus-containing monomer.

Also, the second step of reaction scheme 2 synthesizes a particularbio-derived flame retardant block copolymer by a ring openingpolymerization of a particular biobased cyclic ester (lactide) and aparticular phosphorus-containing polymer (i.e., the bio-derived flameretardant polymer synthesized in the first step of reaction scheme 2).This particular synthesis of this particular bio-derived flame retardantblock copolymer is exemplary. In general, a bio-derived flame retardantblock copolymer in accordance with some embodiments of the presentinvention may be synthesized in the second step of reaction scheme 2using a ring opening polymerization of any suitable biobased cyclicester and any suitable phosphorus-containing polymer.

Biobased diols suitable for reacting with a phosphorus-containingmonomer via a polycondensation reaction to produce a bio-derived flameretardant polymer in accordance with some embodiments of the presentinvention may be either obtained commercially or synthesized. Forexample, suitable biobased diols that may be obtained commerciallyinclude, but are not limited to, isosorbide (as well as the other DAHs),2,5-bis(hydroxymethyl)furan, ethylene glycol, propylene glycol (alsoreferred to as “1,2-propanediol”), 1,3-propanediol, glycerol (alsoreferred to as “glycerin” and “glycerine”), and 2,3-butanediol. Each ofthese diols can be obtained from biomass. Preferably, at least 50% ofthe mass of the biobased diol is obtained directly from a biologicalproduct. More preferably, the entire mass of the biobased diol isobtained directly from a biological product.

Phosphorus-containing monomers suitable for reacting with a biobaseddiol via a polycondensation reaction to produce a bio-derived flameretardant polymer in accordance with some embodiments of the presentinvention may be either obtained commercially or synthesized. Forexample, suitable phosphorus-containing monomers that may be obtainedcommercially include, but are not limited to, phenylphosphonicdichloride, ethylphosphonic dichloride, methylphosphonic dichloride,methylenebis(phosphonic dichloride), phenyl dichlorophosphate (PDCP),ethyl dichlorophosphate, and methyl dichlorophosphate. Generally,suitable phosphorus-containing monomers include, but are not limited to,phosphonic dichlorides, dichlorophosphates, alkyl/aryl phosphonates, orother phosphorus-containing monomers known for flame retardancy (e.g.,phosphinates, phosphonates, phosphate esters, and combinations thereof).

Phosphonic dichlorides and dichlorophosphates are listed among thesuitable phosphorus-containing monomers for purposes of illustration,not limitation. Suitable phosphorus-containing monomers mayalternatively contain other halogen atoms or hydrogen atoms thatparticipate in the polycondensation reaction in lieu of chlorine atoms.

Suitable phosphorus-containing monomers also include (or may besynthesized from) conventional phosphorus-based flame retardants, suchas phosphonates (e.g., dimethyl methyl phosphonate; diethyl ethylphosphonate; dimethyl propyl phosphonate; diethylN,N-bis(2-hydroxyethyl) amino methyl phosphonate; phosphonic acid,methyl(5-methyl-2-methyl-1,3,2-dioxaphosphorinan-5-y) ester,P,P′-dioxide; and phosphonic acid,methyl(5-methyl-2-methyl-1,3,2-dioxaphosphorinan-5-yl)methyl, methylester, P-oxide), phosphate esters (e.g., triethyl phosphate; tributylphosphate; trioctyl phosphate; and tributoxyethyl phosphate), andphosphinates.

A conventional phosphorus-based flame retardant typically includes oneor more of a phosphonate, a phosphate ester, or a phosphinate.Conventional phosphorus-based flame retardants that are phosphonateshave the following generic molecular structure:

where R₁, R₂ and R₃ are organic substituents (e.g., alkyl, aryl, etc.)that may be the same or different.

Conventional phosphorus-based flame retardants that are phosphate estershave the following generic molecular structure:

where R₁, R₂ and R₃ are organic substituents (e.g., alkyl, aryl, etc.)that may be the same or different.

Conventional phosphorus-based flame retardants that are phosphinateshave the following generic molecular structure:

where R₁, R₂ and R₃ are organic substituents (e.g., alkyl, aryl, etc.)that may be the same or different.

One or more of the above conventional phosphorus-based flame retardants(i.e., phosphonate, phosphate ester, and/or phosphinate) and/or otherconventional phosphate-based flame retardants may be functionalized(e.g., halogenated) using procedures well known to those skilled in theart to produce functionalized phosphorus-containing monomers suitablefor reacting with a biobased diol via a polycondensation reaction toproduce a bio-derived flame retardant polymer in accordance with someembodiments of the present invention. Hence, either halogen atoms offunctionalized phosphorus-containing monomers or hydrogen atoms of theconventional phosphorus-based flame retardants may participate in thepolycondensation reaction.

Biobased cyclic ester monomers and oligomers suitable for reacting witha phosphorus-containing polymer via a ring opening polymerization toproduce a bio-derived flame retardant block copolymer in accordance withsome embodiments of the present invention may be either obtainedcommercially or synthesized. For example, suitable biobased cyclicesters that may be obtained commercially include, but are not limitedto, lactide and glycolide. Each of these monomers can be obtained frombiomass. Preferably, at least 50% of the mass of the biobased cyclicester is obtained directly from a biological product. More preferably,the entire mass of the biobased cyclic ester is obtained directly from abiological product.

The third pathway is exemplified below in another non-limiting reactionscheme (i.e., reaction scheme 3). A reaction scheme (reaction scheme 3)follows for synthesizing a bio-derived flame retardant block copolymerin accordance with some embodiments of the present invention through 1.)a ring opening polymerization of a dioxaphospholane monomer to obtain apolyphosphoester and, subsequently, 2.) a ring opening polymerization ofa biobased cyclic ester and the polyphosphoester. In the first step ofreaction scheme 3, a cyclic phosphoester such as2-ethoxy-2-oxy-1,3,2-dioxaphospholane is reacted via a ring openingpolymerization to obtain a polyphosphoester. The first step of reactionscheme 3 is initiated from a diol (e.g., ethylene glycol or othersuitable diol) to ensure that product is hydroxyl-telechelic. In thesecond step of reaction scheme 3, the polyphosphoester and lactide arereacted via ring opening polymerization.

The ring opening polymerizations of reaction scheme 3 may be performedin the same manner as the ring opening polymerizations of reactionschemes 1 and 2.

One skilled in the art will appreciate that any suitable cyclicphosphoester may be utilized in the first step of reaction scheme 3 inlieu of, or in addition to, 2-ethoxy-2-oxy-1,3,2-dioxaphospholane.Suitable cyclic phosphoesters include, but are not limited to,2-ethoxy-2-oxy-1,3,2-dioxaphospholane,2-methyl-2-oxy-1,3,2-dioxaphospholane, and2-ethoxy-4-methyl-2-oxy-1,3,2-dioxaphospholane.

Generally, a flame retardant ABA-type tri-block copolymer in accordancewith some embodiments of the present invention may be synthesized usinga cyclic phosphonate, but only if the first step is initiated from adiol (e.g., ethylene glycol or other suitable diol) to ensure thatproduct is hydroxyl-telechelic.

FIG. 1 is a block diagram illustrating an exemplary printed circuitboard (PCB) 100 having layers of dielectric material that incorporate abio-derived flame retardant block copolymer in accordance with someembodiments of the present invention. In the embodiment illustrated inFIG. 1, the PCB 100 includes one or more module sites 105 and one ormore connector sites 110. The configuration of the PCB 100 shown in FIG.1 is for purposes of illustration and not limitation.

FIG. 2 is a block diagram illustrating an exemplary connector 200 havinga plastic housing 205 and an exemplary plastic enclosure panel 210 thatincorporate a bio-derived flame retardant block copolymer in accordancewith some embodiments of the present invention. In the embodimentillustrated in FIG. 2, the connector 200 is configured to makeelectrical contact with the connector site 110 (shown in FIG. 1) of thePCB 100. Also in the embodiment illustrated in FIG. 2, the connector 200includes a cable 215. The configuration of the connector 200 and theconfiguration of the plastic enclosure panel 210 shown in FIG. 2 are forpurposes of illustration and not limitation.

In accordance with some embodiments of the present invention, abio-derived flame retardant block copolymer is incorporated into theplastic housing 205 to impart flame retardancy. The bio-derived flameretardant block copolymer may be blended, for example, with the basematerial of the plastic housing 205.

In accordance with some embodiments of the present invention, abio-derived flame retardant block copolymer is incorporated into theplastic enclosure panel 210 to impart flame retardancy. The bio-derivedflame retardant block copolymer may be blended, for example, with thebase material of the plastic enclosure panel 210.

One skilled in the art will appreciate that many variations are possiblewithin the scope of the present invention. Thus, while the presentinvention has been particularly shown and described with reference topreferred embodiments thereof, it will be understood by those skilled inthe art that these and other changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. A method of making a flame retardant blockcopolymer, comprising the steps of: providing a biobased cyclic esterand a phosphorus-containing polymer; preparing a ring openingpolymerization reaction product of the phosphorus-containing polymer andthe biobased cyclic ester.
 2. The method as recited in claim 1, whereinthe phosphorus-containing polymer comprises a hydroxyl-telechelic flameretardant biopolymer prepared by a polycondensation reaction of abiobased diol and a phosphorus-containing monomer, wherein at least 50%of the mass of the biobased diol is obtained directly from a biologicalproduct.
 3. The method as recited in claim 2, wherein thehydroxyl-telechelic flame retardant biopolymer is a cyclic phosphonate.4. The method as recited in claim 3, wherein the cyclic phosphonate isrepresented by the following formula:


5. The method as recited in claim 1, wherein the biobased cyclic estercomprises lactide.
 6. The method as recited in claim 1, wherein thebiobased cyclic ester comprises lactide, wherein thephosphorus-containing polymer comprises a hydroxyl-telechelic flameretardant biopolymer, and the ring opening polymerization reactionproduct is represented by the following formula:


7. The method as recited in claim 1, wherein the phosphorus-containingpolymer comprises a polyphosphoester synthesized from a ring openingpolymerization of a dioxaphospholane initiated from a diol.
 8. Themethod as recited in claim 3, wherein the cyclic phosphonate isrepresented by the following formula:


9. The method as recited in claim 1, wherein the biobased cyclic estercomprises lactide, wherein the phosphorus-containing polymer comprises ahydroxyl-telechelic flame retardant biopolymer, and the ring openingpolymerization reaction product is represented by the following formula:


10. The method as recited in claim 7, wherein the polyphosphoester isrepresented by the following formula:


11. The method as recited in claim 1, wherein the biobased cyclic estercomprises lactide, wherein the phosphorus-containing polymer comprises ahydroxyl-telechelic flame retardant biopolymer, and the ring openingpolymerization reaction product is represented by the following formula:


12. A method of making a flame retardant block copolymer, comprising thesteps of: providing a biobased cyclic ester and a phosphorus-containingpolymer, wherein the biobased cyclic ester is selected from a groupconsisting of lactide, glycolide, and combinations thereof, wherein thephosphorus-containing polymer comprises a hydroxyl-telechelic flameretardant biopolymer prepared by a polycondensation reaction of abiobased diol and a phosphorus-containing monomer, wherein the biobaseddiol is selected from a group consisting of 1,4:3,6-dianhydrohexitols(DAHs), 2,5-bis(hydroxymethyl)furan, ethylene glycol, propylene glycol,1,3-propanediol, glycerol, 2,3-butanediol, and combinations thereof, andwherein the phosphorus-containing monomer is selected from a groupconsisting of phenylphosphonic dichloride, ethylphosphonic dichloride,methylphosphonic dichloride, methylenebis(phosphonic dichloride), phenyldichlorophosphate (PDCP), ethyl dichlorophosphate, methyldichlorophosphate, and combinations thereof; preparing a ring openingpolymerization reaction product of the phosphorus-containing polymer andthe biobased cyclic ester.
 13. A method of making a flame retardantblock copolymer, comprising the steps of: providing a biobased cyclicester and a phosphorus-containing polymer, wherein the biobased cyclicester is selected from a group consisting of lactide, glycolide, andcombinations thereof, wherein the phosphorus-containing polymercomprises a polyphosphoester synthesized from a ring openingpolymerization of a dioxaphospholane initiated from a diol, wherein thedioxaphospholane is selected from a group consisting of2-ethoxy-2-oxy-1,3,2-dioxaphospholane,2-methyl-2-oxy-1,3,2-dioxaphospholane,2-ethoxy-4-methyl-2-oxy-1,3,2-dioxaphospholane, and combinationsthereof; preparing a ring opening polymerization reaction product of thephosphorus-containing polymer and the biobased cyclic ester.